Chemical and biological sensors, magnetoresistive sensors, and molecular electronic and optoelectronic devices can be miniaturized using nanowires, mesowires, or carbon nanotubes. Continued advances in nanoscience and nanotechnology require tiny sensors and devices to analyze small sample sizes. Additionally, miniature sensors are useful in cellular and molecular analysis of biological systems. In producing miniature sensors and devices, atom-size gaps and contacts between metal electrodes need to be fabricated.
Atomic-scale contacts between metal electrodes have been traditionally created by mechanically breaking a fine metal wire and separating the two metal electrodes in contact. An apparatus, such as a stepping motor or piezoelectirc transducer, is typically used to control the breaking and separating. The atomic-scale contacts fabricated by mechanical means cannot be removed from the apparatus. Therefore, mass-production and multi-application is impractical.
One non-mechanical method of fabricating atomic-scale contacts uses an aluminum wire anodized locally with an atomic force microscope. However, the use of an atomic force microscope also makes mass-production impractical. A second non-mechanical method uses electrochemical deposition and etching. However, the deposition and etching process does not have a self-termination method, and thus, is also impractical for mass-production.
Conventional microfabrication techniques of gaps between electrodes include electron beam lithography-based techniques. Such lithography-based techniques are not capable of producing molecule-sized or atom-size gaps. The Scanning Probe Microscope and the mechanically controllable break junction techniques have also been used to fabricate two electrodes with a molecular-scale gap. Because of the apparatuses involved with both fabrication methods, mass-production of molecular-scale gaps is impractical.
Electrochemical etching and deposition have also been using to fabricate molecular-scale gaps. However, the method lacks a self-termination mechanism which seriously hinders mass-production of such gaps. One other method of fabricating molecular-scale gaps is based on electromigration. While, using electromigration has a self-termination method, and can achieve a molecule-size gap, the gap width cannot be controlled.
Therefore, a need exists for an apparatus and method for fabricating atomic-scale contacts and gaps that can be easily removed from the apparatus, can create molecule-size gaps while sufficiently controlling gap width, has a built-in self-termination method, and is suitable for mass-fabrication and mass-production, reducing cost of manufacture.